1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube that is capable of reducing a full length of a cathode ray tube by controlling thickness of panel glass, a skirt portion of a panel and a back glass, minimizing a weight of the cathode ray tube and buffering an atmospheric pressure.
2. Description of the Background Art
As shown in FIG. 1, a conventional flat cathode ray tube includes: a panel glass 1 having a fluorescent material coated at the inner surface; a funnel glass 5 adhered at a rear end of a panel glass 1; a shadow mask 2 mounted at an inner side of the panel glass 1 with a certain space therebetween and having a plurality of holes to pass electron beams; an electron gun 3 sealed in the neck portion of the funnel glass 5 and radiating the electron beam; and a deflection yoke 4 for deflecting the electron beams discharged from the electron gun.
The panel glass 1 obtains the minimum space so that the electron beams can accurately light a screen, and maintains a high vacuum state to prevent a collision with other particles. In order to reduce an influence of an electric field to the electron beams, black lead is coated inside the panel glass.
In the cathode ray tube constructed as described above, electrons are activated at a cathode oxide and discharged, and electrons of the fluorescent material are excited with a kinetic energy accelerated by scores of kV accelerating electrode, to emit light. In this respect, about 75˜80% of electrons is blocked by the shadow mask (2) and only the remaining reaches the screen.
At this time, as for the electrons blocked by the shadow mask 2, the kinetic energy of the electrons is mostly transformed to a thermal energy and the remaining is transformed to electromagnetic wave or the like.
The cathode ray tube that uses the electrons as an energy source and displays information on the screen by using the deflection yoke 4 requires a housing structure for obtaining a space in which electrons can move. The housing structure is made of an insulation material, can endure an atmospheric pressure, should have a little outgassing in collision with electrons, should be transparent and stable physically and chemically even at a temperature process of 370˜450° C.
Accordingly, the housing structure of the most cathode ray tube is made of glass, a material that satisfies the above indicated conditions.
However, since the conventional cathode ray tube has one place of energy source for displaying information on the screen and uses only one deflection yoke 4, it is difficult to implement a deflection sensitivity of above a certain level.
Accordingly, in order to display accurate information on the screen, comparatively large internal space is necessary, which is obtained by the panel glass 1 and the funnel glass 5.
In order to prevent deformation and damage due to the atmospheric pressure working and stress occurrence, the panel glass 1 should have a certain thickness, and the funnel glass 5 has a smooth curved form in view of obtaining a space and coping with a vacuum strength.
If the width of the portion where the funnel glass 1 and the panel glass 5 are sealed is thinner than the thickness of the panel glass 1, the thickness of the funnel glass 5 is thinner than the panel glass 1 on the whole.
In the cathode ray tube with the above described structure, even if the panel glass 1 receives a force vertically by atmospheric pressure, the force is transmitted to the funnel glass 5, and the force which has been transferred to the funnel glass 5 is distributed to the funnel glass 5 in a form of hemisphere, thereby preventing deformation of the panel glass 1.
FIGS. 4A and 4B are graphs showing a ratio of a minimum thickness of the panel glass 1 to a minimum thickness of a skirt portion of the panel glass 1, of which FIG. 4A shows a cathode ray tube having the width-to-length ratio of a screen is 4:3 and FIG. 4B shows a cathode ray tube having the width-to-length ratio of 16:9.
As shown in FIGS. 4A and 4B, in a size more than 8 inches, the ratio of the minimum thickness of the panel glass 1 to the minimum thickness of the skirt portion of the panel glass 1 is above 1.15, and this ratio is increased for a flat type cathode ray tube.
However, such a cathode ray tube has a great volume due to the curved funnel glass 5 and very complicated internal structure.
Thus, in an effort to solve the problem, instead of the funnel glass 5 as shown in FIG. 2, a back glass 6 is used to form a flat type cathode ray tube with a reduce the front length.
As shown in FIG. 3, the flat type cathode ray tube includes, a cathode 8 positioned between the panel 1 glass and the back glass 6 and generating electron beams, an electrode 9 for emitting an electron beam at the entire surface of the cathode 8, a control electrode 10 for controlling the electron beam; two electrodes 11 and 12 for focussing the electron beam, a horizontal deflection electrode 13 and a vertical deflection electrode 15 for deflecting the electron beam.
Reference numeral 7 denotes a back electrode and 14 denotes a Gshield.
The flat type cathode ray tube adopts a deflection method of a passive driving method, of which the panel glass 1, the back glass 6 and the skirt portion 1a have the same thickness.
In this respect, however, the skirt portion 1a makes a working point of every force applied to the atmospheric pressure, and in case of the cathode ray tube having the short depth, there is a limitation that the skirt portion 1a distributes a force, resulting in that the skirt portion 1a is deformed partially and seriously, and in a worse case, the skirt portion 1a is damaged.